Vacuum Leak Only While Cold??

[TurboTsiThatFly]

my vacuum gauge reads at idle normally around19 to 20 vac. but here recently when i go to crank my car in the morning the vacuum only shows about 17 to 18 of vac.. and the car cranks like crap. and runs like it too only for a minute though. but after the car warms up it shows good vac or back to normal range(19 to 20 vac). i know its a vacuum leak but where should i start looking. Ive checked the fpr and lines around my boost gauge. i replaced the only hose i could see would be leaking. and it didn't help out any. also my brand new clutch is slipping but it has fluid and everything. i think it might just need adjustment cause the release point of the clutch is at the top. what do you guys think?

 

[TurboTsiThatFly]

Also what size is the factory vacuum hoses?

 

[Avionixx]

Do a boost leak test. Yea, so they call it a boost leak test, but it tests for vacuum leaks too.

Not sure what size the vacuum lines are exactly, but if I had to guess I'd say between 5/32" and 3/16". 1/8" is probably too small.